Mask, method of manufacturing a mask, method of manufacturing an organic electroluminescence device, and organic electroluminescence device

ABSTRACT

A mask is disclosed for use in forming a thin-layer pattern of an organic electroluminescence element having high-precision pixels. The mask is manufactured by wet-etching a (100) silicon wafer (single crystal silicon substrate)  1  in a crystal orientation-dependent anisotropic fashion so as to form through-holes  11  having (111)-oriented walls  11   a  serving as apertures corresponding to a thin-layer pattern to be formed.

[0001] This is a Continuation of application Ser. No. 10/053,907 filedJan. 24, 2002. The entire disclosure of the prior application is herebyincorporated by reference herein in its entirety.

TECHNICAL FIELD

[0002] The present invention relates to a mask used for directly forminga thin layer pattern on the surface of a layer, a method ofmanufacturing such a mask, a method of manufacturing an organicelectroluminescence (EL) device using such a mask, and an organic ELdevice manufactured using such a method.

BACKGROUND ART

[0003] In recent years, increasingly rapid advancements have been madein the art of an organic electroluminescence display device usingorganic electroluminescence elements (light emitting elements having astructure in which a luminescent layer formed of an organic material isdisposed between an electrode and a cathode electrode) disposed forrespective pixels. The organic electroluminescence display devices areexpected to be used as emissive-type displays instead of liquid crystaldisplay devices. Known materials for forming a luminescent layer in anorganic electroluminescence element include an aluminum quinolinocomplex (Alq3) that is a low-molecular organic material and polyp-phenylenevinylene that is a macromolecular organic material.

[0004] A technique of forming a luminescent layer using a low-molecularorganic material by means of vacuum evaporation is disclosed, forexample, in Appl. Phys. Lett. 51(12), Sep. 21, 1987, p. 913. A techniqueof forming a luminescent layer using a macromolecular organic materialby means of a coating process is disclosed, for example, in Appl. Phys.Lett. 71(1), Jul. 7, 1997, p. 34.

[0005] When forming a luminescent layer using a low-molecular organicmaterial by means of vacuum evaporation, a metal mask (made of a metalsuch as stainless steel so as to have apertures corresponding to athin-layer pattern to be formed) is conventionally used. In thistechnique, a thin-layer pattern corresponding to pixels can be directlyformed on a substrate surface. In this technique, in contrast to atechnique using a conjunction of a photolithographic process and anetching process in which a thin layer is first formed over the entiresurface of a substrate and then the thin layer is patterned byphotolithographic and etching processes, a thin layer having a desiredpattern is directly formed using a metal mask.

[0006] However, the technique using a metal mask has the followingproblems.

[0007] If, in order to manufacture apertures so as to preciselycorrespond to a thin-layer pattern with a very small size, a metal maskhaving a small thickness is employed or if the distance between adjacentapertures is reduced, the mask can be bent or deformed during a process.In order to prevent the mask from being bent or deformed, it is requiredto apply a tensile force to the mask during the layer formation process.However, the tensile force can cause the apertures to be deformed. Thus,even if the metal mask is placed at a correct location, there is apossibility that the locations of the apertures deviate from the correctlocations corresponding to the thin-layer pattern to be formed on asubstrate.

[0008] A metal mask may be manufactured by forming apertures in a metalplate using a wet etching technique, a plating technique, a pressingtechnique, or a laser beam processing technique. However, in theseconventional techniques, the size accuracy of apertures is limited to ±3μm, which is not sufficient to manufacture high-precision pixels.

DISCLOSURE OF INVENTION

[0009] In view of the above, it is an object of the present invention toprovide a mask for use in directly producing a thin-film pattern on asubstrate surface without having to perform a photolithographic process(that is, producing a thin film having a desired pattern on a substratesurface), having mask apertures formed with high enough accuracy (±1 μm,for example) to form high-precision pixels without causing the mask tobe bent or deformed and without having to applying a tensile force tothe mask during a thin-film formation process.

[0010] It is another object of the present invention to provide anorganic electroluminescence display device having high-precision pixelsmanufactured by forming a thin-layer pattern serving as a layer (such asa luminescent layer) of the organic electroluminescence element using amask according to the present invention.

[0011] According to an aspect of the present invention, there isprovided a mask for use in manufacturing a thin-layer pattern serving asa layer of an organic electroluminescence element by means of vacuumevaporation, the mask having an aperture corresponding to the thin-layerpattern, the mask being formed of single crystal silicon and having athrough-hole serving as the aperture formed by means of anisotropic wetetching using a crystal orientation dependence.

[0012] According to another aspect of the present invention, there isprovided a mask for use in manufacturing a thin-layer pattern serving asa layer of an organic electroluminescence element by means of vacuumevaporation, the mask having an aperture corresponding to the thin-layerpattern, the mask being formed of single crystal silicon so as to have amask surface formed by a (100) surface of the single crystal silicon andhave a through-hole with (111)-oriented walls serving as the aperture.

[0013] According to still another aspect of the present invention, thereis provided a mask for use in manufacturing a thin layer having apredetermined pattern on a substrate surface, the mask having anaperture corresponding to the pattern, the mask being formed of singlecrystal silicon; the size of the aperture changing in a mask thicknessdirection such that the size has, at a boundary position, a minimumvalue corresponding to the size of the pattern and the size increasingtoward both mask surfaces; and the distance from the boundary positionto one mask surface and the distance from the boundary position to theopposite mask surface being different from each other.

[0014] In this mask according to the present invention, preferably, themask surface being formed by a (100)-surface of single crystal silicon,and the aperture including two wall portions that are tapered inopposite directions and that expand from the boundary position towardrespective mask surfaces opposite to each other, and at least one wallportion being oriented in a (111)-direction.

[0015] In this mask according to the present invention, the mask havinga thin portion in which the aperture is formed and a thick portion inwhich no aperture is formed. Preferably, the mask according to thepresent invention may be manufactured by a process having four featuresdescribed below.

[0016] Firstly, a thin portion having a uniform thickness is formed in apartial substrate area by etching a single crystal silicon substratehaving a (100)-oriented crystal surface in a thickness direction of thesingle crystal silicon substrate; a first protective layer patternhaving a through-hole corresponding to the aperture is formed on a firstsurface of the thin portion; and a second protective layer patternhaving a recessed portion is formed at a location corresponding to thelocation of the aperture, on a second surface of the thin portion.

[0017] Secondly, after the above-described process, a through-hole isformed in the thin portion at a location corresponding to the locationof the aperture by means of anisotropic wet etching using the crystalorientation dependence such that the aperture size of the through-holeis greater at the first surface than at the boundary position and issmaller at the second surface than at the boundary position and than thesize of the recessed portion.

[0018] Thirdly, the second protective layer pattern is converted into athird protective layer pattern by performing wet etching such that thebottom of the recessed portion is perforated so that the recessedportion becomes a through-hole while maintaining the protective layer onthe first surface.

[0019] Fourthly, the thin portion is anisotropic wet-etched using thecrystal orientation dependence such that a part of the thin portionexposed via the through-hole formed in the third protection layerpattern is etched until the aperture size at the boundary positionbecomes equal to a predetermined size.

[0020] According to still another aspect of the present invention, thereis provided a method of manufacturing a mask for use in manufacturing athin-layer pattern serving as a layer of an organic electroluminescenceelement by means of vacuum evaporation, the mask having an aperturecorresponding to the thin-layer pattern, the method comprising: a stepof forming a through-hole as the aperture in which a single crystalsilicon substrate having a (100)-oriented crystal surface by means ofanisotropic wet etching using the crystal orientation dependence suchthat a through-hole having a (111)-oriented wall.

[0021] The method may preferably further comprise a step of thinning thesingle crystal silicon substrate by etching in a thickness directionthereof such that a thin portion having a uniform thickness is formed inan partial area of the single crystal silicon substrate, after the stepof thinning the single crystal silicon substrate, the through-hole beingformed in the thin portion by means of the anisotropic wet etching usingthe crystal orientation dependence.

[0022] According to another aspect of the present invention, there isprovided a method of manufacturing a mask for use in manufacturing athin layer having a predetermined pattern on a substrate surface, themask having a aperture corresponding to the pattern, the methodcomprising: a step of preparing a substrate including a base substrate,an insulating layer formed on one surface of the base substrate, and asingle crystal silicon layer formed on the insulating layer; a step ofremoving the base substrate such that at least a partial area of thebase substrate is removed over the entire thickness of the basesubstrate; and a step of anisotropic etching the single crystal siliconlayer remaining in the area from which the base substrate has beenremoved, so as to form a through-hole serving as the aperture in thesingle crystal silicon layer.

[0023] According to still another aspect of the present invention, thereis provided a method of manufacturing an organic electroluminescencedevice including a step of forming a thin layer pattern serving as alayer of the organic electroluminescence element by performing vacuumevaporation using a mask according to the present invention or a maskmanufactured according to a mask production method according to thepresent invention.

[0024] According to still another aspect of the present invention, thereis provided an organic electroluminescence device manufactured by anorganic electroluminescence device production method according to thepresent invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] FIGS. 1(a) to 1(f) are diagrams illustrating a mask and a methodof manufacturing the same according a first embodiment of the presentinvention.

[0026] FIGS. 2(a) to 2(d) are diagrams illustrating a mask and a methodof manufacturing the same according a second embodiment of the presentinvention.

[0027] FIGS. 3(a) to 3(d) are diagrams illustrating a mask and a methodof manufacturing the same according a second embodiment of the presentinvention.

[0028] FIGS. 4(a) to 4(e) are diagrams illustrating a mask and a methodof manufacturing the same according a third embodiment of the presentinvention.

[0029] FIGS. 5(a) to 5(f) are diagrams illustrating a mask and a methodof manufacturing the same according a fourth embodiment of the presentinvention.

[0030] FIGS. 6(a) to 6(e) are diagrams illustrating a mask and a methodof manufacturing the same according a fifth embodiment of the presentinvention.

[0031] FIGS. 7(a) to 7(f) are diagrams illustrating a mask and a methodof manufacturing the same according a sixth embodiment of the presentinvention.

[0032] FIGS. 8(a) to 8(c) are diagrams illustrating a method ofmanufacturing an organic electroluminescence device according to anembodiment of the present invention.

[0033] FIGS. 9(a) to 9(c) are diagrams illustrating a method ofmanufacturing an organic electroluminescence device according to anotherembodiment of the present invention.

[0034]FIG. 10 is a cross-sectional view illustrating an example of amask having a raised portion which is formed during a process of a maskand which is effectively used as a mask supporting portion during aprocess of manufacturing an organic electroluminescence device accordingto a method of the present invention.

[0035]FIG. 11 is a cross-sectional view illustrating an example of amask having a raised portion which is formed during a process of a maskand which is effectively used as a substrate supporting portion during aprocess of manufacturing an organic electroluminescence device accordingto a method of the present invention.

[0036]FIG. 12(a) is a plan view of a mask according to a seventhembodiment of the present invention, and FIG. 12(b) is a cross-sectionalview taken along line B-B of FIG. 12(a).

[0037] FIGS. 13(a) to 13(f) are diagrams illustrating a first method ofmanufacturing a mask according to the seventh embodiment of the presentinvention.

[0038] FIGS. 14(a) to 14(f) are diagrams illustrating a second method ofmanufacturing a mask according to the seventh embodiment of the presentinvention.

[0039]FIG. 15 is a cross-sectional view illustrating a method ofmanufacturing an organic electroluminescence device according to a thirdembodiment of the present invention.

[0040]FIG. 16 is a cross-sectional view illustrating the method ofmanufacturing the organic electroluminescence device according to thethird embodiment of the present invention.

[0041]FIG. 17 is a cross-sectional view illustrating the method ofmanufacturing the organic electroluminescence device according to thethird embodiment of the present invention.

[0042]FIG. 18 is a cross-sectional view illustrating a method ofmanufacturing an organic electroluminescence device according to afourth embodiment of the present invention.

[0043]FIG. 19 is a cross-sectional view illustrating the method ofmanufacturing the organic electroluminescence device according to thefourth embodiment of the present invention.

[0044]FIG. 20 is a cross-sectional view illustrating the method ofmanufacturing the organic electroluminescence device according to thefourth embodiment of the present invention.

[0045]FIG. 21 is a cross-sectional view illustrating the method ofmanufacturing the organic electroluminescence device according to thefourth embodiment of the present invention.

[0046]FIG. 22 is a cross-sectional view illustrating the method ofmanufacturing the organic electroluminescence device according to thefourth embodiment of the present invention.

[0047]FIG. 23 is a perspective view showing the structure of a personalcomputer that is one of electronic devices using an organicelectroluminescence device according to the present invention.

[0048]FIG. 24 is a perspective view showing the structure of a portabletelephone that is one of electronic devices using an organicelectroluminescence device according to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

[0049] Embodiments of the present invention are described below.

[0050] [Method of Manufacturing a Mask According to a First Embodiment]

[0051] A mask and a method of manufacturing it according to a firstembodiment of the present invention are described below with referenceto FIG. 1.

[0052] First, as shown in FIG. 1(a), a silicon wafer (single crystalsilicon substrate) 1 with a surface orientation of (100) is prepared. Asilicon oxide layer 2 is then formed over the entire surface of thewafer 1 by means of a CVD technique. Openings 21 are then formed in thesilicon oxide layer 2 on one surface (the upper surface in this specificexample) of the wafer 1 such that the shapes of the resultant openings21 correspond to the shapes (such as a rectangle or a square, while theopenings 21 of the present example have a square shape) of openings of amask and such that the surface of the wafer 1 is exposed via theopenings 21. The formation of the openings 21 may be accomplished bymeans of a conjunction of a photolithographic process and a dry etchingprocess. FIG. 1(b) shows the structure obtained at this stage of theprocess.

[0053] The wafer 1 is then soaked in an aqueous solution of potassiumhydroxide for a predetermined time so that the silicon surface exposedvia the openings 21 is anisotropically wet-etched using etching propertydependence on the crystal orientation. As a result, through-holes 11each having four (111)-oriented walls 11 a are formed in the wafer 1, atlocations corresponding to the openings 21.

[0054]FIG. 1(c) shows the structure obtained at this stage of theprocess. FIG. 1(d) is a plan view of a through-hole 11 formed in thewafer 1, viewed from the upper side of the wafer 1 (that is, from theside where the openings 21 are formed), wherein FIG. 1(c) is across-sectional view taken along a line A-A of FIG. 1(d).

[0055] As shown in FIGS. 1(c) and 1(d), the through-holes 11 are formedsuch that four walls 11 a of each through-hole 11 are oriented in (111)directions at an angle of 54.74° (θ=54.74°) to the (100)-surface of thewafer 1 and such that the distance between two opposing walls 11 a isgreatest at the upper surface of the wafer 1 and decreases toward thelower surface of the wafer 1 (that is, the through-holes 11 aretapered). That is, each through-hole 11 has a shape that is manufacturedwhen an apex portion of a quadrangular pyramid whose base corresponds toa square of an opening 21 formed in the silicon oxide 2 is cut along aplane parallel with the base plane.

[0056] Thus, the upper-side opening 11 b of each through-hole 11 has asquare shape that is substantially equal in size to a correspondingopening 21 formed in the silicon oxide layer 2, and the lower-sideopening 11 c of each through-hole 11 has a square shape that is smallerthan the opening 11 b on the upper side of the wafer.

[0057] The silicon oxide layer 2 is then removed by soaking the wafer 1in an aqueous solution of a hydrofluoric acid-base etchant. FIG. 1(e)shows the structure obtained at this stage of the process.

[0058] A silicon oxide layer 3 with a uniform thickness is then formedsuch that the entire surface of the silicon wafer 1, including the walls11 a of the respective through-holes 11, is covered with the siliconoxide layer 3. The silicon oxide layer 3 may be formed by means ofthermal oxidation. FIG. 1(f) shows the structure obtained at this stageof the process.

[0059] Thus, a mask is obtained which is made of single crystal siliconso as to have a mask surface formed by a (100)-surface of the singlecrystal silicon and have apertures with walls oriented in(111)-directions formed by through-holes 11. Because this mask is madeof single crystal silicon, even when the mask thickness and theopening-to-opening distance are small, the mask can be handled withoutcausing bending or deformation. Bending does not occur even if notensile force is applied during the layer formation process. Theopenings can be formed with high enough precision to form high-precisionpixels.

[0060] Because the through-holes 11 formed by the present method has atapered structure, if the mask is placed such that a mask surface (lowerwafer surface at which opening ends 1 c are located) at which thethrough-holes 11 have smaller aperture sizes than at the oppositesurface is brought into proximity to a substrate surface on which athin-layer pattern is to be formed, it is possible to prevent theresultant thin-layer pattern from becoming thin at its edge.

[0061] In order to use the mask in the above-described manner, the sizeof the smaller end of each opening 11 c should correspond to the size ofthe thin-layer pattern to be formed. Because the size of each opening 11c is determined by the size of the corresponding opening 21 formed inthe silicon oxide layer 2 and by the thickness of the wafer 1, the sizeof each opening 21 formed in the silicon oxide layer 2 and the thicknessof the wafer 1 should be selected so that the size of each opening 11 ccorresponds to the size of the thin-layer pattern to be formed.

[0062] The silicon oxide layer 3 serves as a protective layer of themask, and thus the mask does not necessarily need to have the siliconoxide layer 3. That is, the final structure of the mask may be similarto that shown in FIG. 1(e). In this case, the size of the opening 21formed in the silicon oxide layer 2 should be determined so that thesize of the opening 11 c of the through-hole 11 becomes equal to thesize of the thin-layer pattern to be formed.

[0063] [Method of Manufacturing a Mask According to a Second Embodiment]

[0064] A mask and a method of manufacturing it according to a secondembodiment of the present invention are described below with referenceto FIGS. 2 and 3.

[0065] First, as shown in FIG. 2(a), a (100) silicon wafer (singlecrystal silicon substrate) 1 with a thickness equal to that employed inthe first embodiment is prepared. A silicon oxide layer 2 is then formedover the entire surface of the wafer 1 by means of a CVD technique. Anopening 22 is then formed in the silicon oxide layer 2 on one surface(lower surface in this specific example) of the wafer 1 such that thelower surface of the wafer 1 is exposed via the opening 22 except for aperipheral area of the lower surface. The formation of the openings 22may be accomplished by means of a conjunction of a photolithographicprocess and an etching process. FIG. 2(b) shows the structure obtainedat this stage of the process.

[0066] The wafer 1 is then soaked in an aqueous solution of potassiumhydroxide for a predetermined time so that the silicon surface exposedvia the openings 22 is wet-etched in a crystal orientation-dependentanisotropic fashion. As a result, a recessed portion 12 having(111)-oriented walls 12 a is formed in the wafer 1 at a locationcorresponding, to the opening 22, and thus a thin portion 13 with auniform thickness (20 μm, for example) is formed in the wafer 1 at thebottom of the opening 22, and a raised portion 14 is formed in theperipheral area on the upper surface of the wafer 1. FIG. 2(c) shows thestructure obtained at this stage of the process.

[0067] The time during which the wafer 1 is soaked in the aqueoussolution of potassium hydroxide is determined, taking into account theoriginal thickness of the wafer 1, so that the thickness of the thinportion 13 has a desired value. The walls 12 a of the recessed portion12, as with the walls 11 a of the through-holes 11 according to thefirst embodiment, are oriented in (111) directions at an angle of 54.74°to the (100)-surface of the wafer 1. However, in this case, the distancebetween two opposing walls 11 a is greatest at the lower surface of thewafer 1 and decreases toward the upper surface of the wafer 1 (that is,the recessed portion 12 is tapered).

[0068] A silicon oxide layer 2 a is then formed by means of thermaloxidation such that the walls 12 a and the bottom 12 b of the recessedportion 12 is covered with the silicon oxide layer 2 a. FIG. 2(d) showsthe structure obtained at this stage of the process.

[0069] Thereafter, rectangular-shaped openings 21 corresponding toopenings of the mask to be manufactured are formed in the silicon oxidelayer 2 on the upper surface (opposite to the surface where the recessedportion 12 is formed) of the thin portion 13 such that the surface ofthe wafer 1 is exposed via the openings 21. The formation of theopenings 21 may be accomplished by means of a conjunction of aphotolithographic process and a dry etching process. FIG. 3(a) shows thestructure obtained at this stage of the process.

[0070] The wafer 1 is then soaked in an aqueous solution of potassiumhydroxide for a predetermined time so that the silicon surface exposedvia the openings 21 is anisotropically wet-etched using etching propertydependence on the crystal orientation. As a result, through-holes 11each having four (111)-oriented walls 11 a are formed in the wafer 1, atlocations corresponding to the openings 21. FIG. 3(b) shows thestructure obtained at this stage of the process.

[0071] As in the first embodiment, the through-holes 11 are formed suchthat four walls 11 a of each through-hole 11 are oriented in (111)directions at an angle of 54.74° to the (100)-surface of the wafer 1 andsuch that the distance between two opposing walls 11 a is greatest atthe upper surface of the wafer 1 and decreases toward the lower surfaceof the wafer 1 (that is, the through-holes 11 are tapered).

[0072] Thus, the open end, on the upper side of the thin portion 13, ofeach through-hole 11 has a rectangular shape with a size substantiallyequal to the size of the corresponding opening 21 formed in the siliconoxide layer 2, and the open end, on the lower side of the thin portion13, of each through-hole 11 has a rectangular shape with a size smallerthan the size of the open end on the upper side.

[0073] The silicon oxide layer 2 is then removed by soaking the wafer 1in an aqueous solution of a hydrofluoric acid-base etchant. FIG. 3(c)shows the structure obtained at this stage of the process.

[0074] A silicon oxide layer 3 with a uniform thickness is then formedsuch that the entire surface of the silicon wafer 1, including the walls11 a of the respective through-holes 11 and the bottom of the recessedportion 12, is covered with the silicon oxide layer 3. The silicon oxidelayer 3 may be formed by means of thermal oxidation. FIG. 3(d) shows thestructure obtained at this stage of the process.

[0075] Thus, a mask is obtained which is made of single crystal siliconsuch that the mask surface is formed by a (100)-surface of the singlecrystal silicon, each through-hole 11 formed in the thin portion 12formed in the center of the mask surface has walls oriented in(111)-directions, and the raised portion 14 is formed in the peripheralarea on the same side as that at which each through-hole 11 has asmaller aperture size than at the opposite side.

[0076] Because this mask is made of single crystal silicon, even whenthe mask thickness and the opening-to-opening distance are small, themask can be handled without causing bending or deformation. Bending doesnot occur even if no tensile force is applied during the layer formationprocess. The openings can be formed with high enough precision to formhigh-precision pixels.

[0077] Because the each through-hole 11 formed by the present method hasa tapered structure, if the mask is placed such that a mask surface atwhich each through-hole 11 has a smaller aperture size than at theopposite surface is brought into proximity to a substrate surface onwhich a thin-layer pattern is to be formed, it is possible to preventthe resultant thin-layer pattern from becoming thin at its edge.

[0078] In order to use the mask in the above-described manner, the sizeof the smaller opening end of each through-hole 11 should correspond tothe size of the thin-layer pattern to be formed. Because the size of thesmaller opening end is determined by the size of the correspondingopening 21 formed in the silicon oxide layer 2 and by the thickness ofthe thin portion 13, the size of the opening 21 formed in the siliconoxide layer 2 should be determined, taking into account the thickness ofthe thin portion 13, such that the size of the thin-layer pattern to beformed corresponds to the size of the open end of the correspondingthrough-hole 11.

[0079] As with the mask according to the first embodiment, the maskaccording to the present embodiment does not necessarily need to havethe silicon oxide layer 3. That is, the final structure of the mask maybe similar to that shown in FIG. 3(c). Furthermore, the raised portion14 may or may not be removed. In the case where some or entire raisedportion 14 is left, the thickness or the shape of the raised portion 14may be adapted to support a substrate on which the thin layer pattern isto be formed. Even in the case where the raised portion 14 is finallyremoved, the raised portion 14 serves as a supporting portion during theprocess in which the mask is manufactured.

[0080] In the mask manufactured according to the present embodiment inwhich the through-holes 11 are formed in the thin portion 13, if thethickness of the thin portion 13 is set to be small enough, openings canbe precisely formed in the mask such the size of each opening accuratelycorresponds to a fine thin-layer pattern. Thus fine opening preciselycorresponding to the thin-layer pattern to be formed can be easilyformed in the mask, even when a silicon wafer with a rather largethickness such as 500 μm is used.

[0081] [Method of Manufacturing a Mask According to a Third Embodiment]

[0082] A mask and a method of manufacturing it according to a thirdembodiment of the present invention are described below with referenceto FIG. 4.

[0083] First, an SOI (Silicon On Insulator) substrate 5 composed of asingle crystal silicon substrate 51 located at the bottom, a siliconoxide layer (insulating layer) 52 formed on the single crystal siliconsubstrate 51, and a single crystal silicon layer 53 formed on thesilicon oxide layer 52 is prepared.

[0084] SOI substrates 5 having a single crystal silicon layer 53 with athickness selected from a wide range can be commercially available. Forexample, the thickness of the single crystal silicon substrate 51 may beequal to 500 μm, the thickness of the silicon oxide layer 52 may beequal to 1 μm, and the thickness of the single crystal silicon layer 53may be equal to 20 μm. A silicon oxide layer 2 is then formed over theentire surface of the SOI substrate 5 by means of a CVD technique. FIG.4(a) shows the structure obtained at this stage of the process.

[0085] Thereafter, by means of a conjunction of a photolithographicprocess and a dry etching process, a plurality of square-shaped openings21 corresponding to apertures to be manufactured are formed in thesilicon oxide layer 2 on the single crystal silicon layer 53 and anopening 22 is formed in the silicon oxide layer 2 on the siliconsubstrate 51 such that the surface of the silicon substrate 51 isexposed via the opening 22 except for a peripheral area. FIG. 4(b) showsthe structure obtained at this stage of the process.

[0086] The SOI substrate 5 is then soaked in an aqueous solution ofpotassium hydroxide for a predetermined time so that the silicon surfaceexposed via the openings 21 and the silicon surface exposed via theopening 22 are anisotropically wet-etched using etching propertydependence on the crystal orientation. The time during which the SOIsubstrate 5 is soaked in the aqueous solution of potassium hydroxide isdetermined so that the exposed portions of the single crystal siliconsubstrate 51 are entirely etched in the thickness direction and thusthrough-holes 51 a are formed in the single crystal silicon substrate51.

[0087] As a result, a through-hole 511 having a tapered shape whosewalls 511 a are oriented in (111)-directions is formed in the singlecrystal silicon substrate 51, at a location corresponding to the opening22, and through-holes 531 having a tapered shape whose walls 531 a areoriented in (111)-directions are formed in the single crystal siliconlayer 53, at locations corresponding to the openings 21. The peripheralportion of the single crystal silicon substrate 51 remains without beingetched, and thus a raised portion 512 is formed. FIG. 4(c) shows thestructure obtained at this stage of the process.

[0088] In order to use the resultant structure as a mask in such amanner that the mask is placed such that the silicon oxide layer 52 onthe single crystal silicon layer 53 is brought into proximity to asurface of a substrate on which a thin-layer pattern is to be formed, itis required that the aperture size of each through-hole 531 at aboundary with the silicon oxide layer 52 should correspond to thethin-layer pattern to be formed. Because the apertures size of eachthrough-hole 531 is determined by the size of the corresponding opening21 formed in the silicon oxide layer 2 and by the thickness of thesingle crystal silicon layer 53, it is required that the size of eachopening 21 formed in the silicon oxide layer 2 should be determinedtaking into account the thickness of the single crystal silicon layer 53so that the aperture size of each through-hole 531 at the boundary withthe silicon oxide layer 52 corresponds to the thin-layer pattern to beformed.

[0089] The silicon oxide layer 2 and the portion of the silicon oxidelayer 52 exposed through the through-hole 511 are then removed bysoaking the SOI substrate 5 in an aqueous solution of a hydrofluoricacid-base etchant. FIG. 4(d) shows the structure obtained at this stageof the process.

[0090] A silicon oxide layer 3 with a uniform thickness is then formedsuch that the entire surface of the SOI substrate 5, including the walls511 a and 531 a of the respective through-holes 511 and 531, is coveredwith the silicon oxide layer 3. The silicon oxide layer 3 may be formedby means of thermal oxidation. FIG. 4(e) shows the structure obtained atthis stage of the process.

[0091] Thus, a mask is obtained which is made of single crystal siliconsuch that a mask surface is formed by a (100)-surface of the singlecrystal silicon, the mask has apertures formed by the through-holes 531whose walls are oriented in (111)-directions and which are formed in thethin portion (that remains after etching the single crystal siliconsubstrate 51) in the center of the mask, and the raised portion 512 isformed on the same side as that where the through-holes 531 have smalleraperture sizes than on the opposite side.

[0092] Because this mask is made of single crystal silicon, even whenthe mask thickness and the opening-to-opening distance are small, themask can be handled without causing bending or deformation. Bending doesnot occur even if no tensile force is applied during the layer formationprocess. The openings can be formed with high enough precision to formhigh-precision pixels.

[0093] Furthermore, because the apertures are formed by the taperedthrough-holes 531, if the mask is placed such that a mask surface atwhich the through-holes 531 have smaller aperture sizes than at theopposite surface is brought into proximity to a substrate on which thethin-layer pattern is to be formed, it is possible to prevent an edgeportion of the resultant thin-layer pattern from becoming thinner thanthe main portion thereof.

[0094] As with the mask according to the first embodiment, the maskaccording to the present embodiment does not necessarily need to havethe silicon oxide layer 3. That is, the final structure of the mask maybe similar to that shown in FIG. 4(d). Furthermore, the raised portion512 may or may not be entirely or partially removed. In the case wheresome or entire raised portion 512 is left, the thickness or the shape ofthe raised portion 512 may be adjusted so as to support a substrate onwhich the thin layer pattern is to be formed. Even in the case where theraised portion 512 is finally removed, the raised portion 14 serves as asupporting portion during the process in which the mask is manufactured.

[0095] In the mask manufactured according to the present embodiment, theapertures corresponding to the thin-layer pattern to be formed areformed by the through-holes 531 formed in the single crystal siliconlayer 53 of the SOI substrate 5, and thus, if the single crystal siliconlayer 53 of the SOI substrate 5 is thin enough, it is possible torealize apertures so as to precisely correspond to the thin-layerpattern to be formed even when the thin-layer pattern has a very smallsize.

[0096] [Method of Manufacturing a Mask According to a Fourth Embodiment]

[0097] A mask and a method of manufacturing it according to a fourthembodiment of the present invention are described below with referenceto FIG. 5.

[0098] First, as in the third embodiment described above, an SOI(Silicon On Insulator) substrate 5 composed of a single crystal siliconsubstrate 51 located at the bottom, a silicon oxide layer (insulatinglayer) 52 formed on the single crystal silicon substrate 51, and asingle crystal silicon layer 53 formed on the silicon oxide layer 52 isprepared. A silicon oxide layer 2 is then formed over the entire surfaceof the SOI substrate 5. FIG. 5(a) shows the structure obtained at thisstage of the process.

[0099] Thereafter, by means of a conjunction of a photolithographicprocess and a dry etching process, an opening 22 is formed in thesilicon oxide layer 2 on the single crystal silicon substrate 51 suchthat the surface of the single crystal silicon substrate 51 is exposedvia the opening 22 except for a peripheral area. The SOI substrate 5 isthen soaked in an aqueous solution of potassium hydroxide for apredetermined time so that the portion of the single crystal siliconsubstrate 51 exposed via the opening 22 is anisotropically wet-etchedusing etching property dependence on the crystal orientation so that athrough-hole 511 having walls 511 a oriented in (111)-directions isformed in the single crystal silicon substrate 51. A peripheral portionof the single crystal silicon substrate 51 remains without being etched,and thus a raised portion 512 is formed. FIG. 5(b) shows the structureobtained at this stage of the process.

[0100] Thereafter, by means of a conjunction of a photolithographicprocess and a dry etching process, a plurality of square-shaped openings21 corresponding to apertures to be manufactured are formed in thesilicon oxide layer 2 on the single crystal silicon layer 53. FIG. 5(c)shows the structure obtained at this stage of the process.

[0101] Thereafter, by means of ICP-RIE (Inductively Coupled PlasmaReactive Ion Etching) technique, portions of the single crystal siliconlayer 53 exposed via the openings 21 are anisotropically dry-etchedunder a proper etching condition so that through-holes 532 are formed inthe single crystal silicon layer 53, at locations corresponding to theopenings 21. The cross section, taken at any position in the depthdirection, of each resultant through-hole 532 has a square shape equalin size to the corresponding opening 21 formed in the silicon oxidelayer 2. FIG. 5(d) shows the structure obtained at this stage of theprocess.

[0102] In the present embodiment, the size of each square-shaped opening21 formed in the silicon oxide layer 2 is selected so as to correspondto a square of a thin-layer pattern to be formed. The techniqueaccording to the present embodiment may also be employed when thethin-layer pattern to be formed has an arbitrary shape other than asquare or a rectangle.

[0103] Thereafter, the silicon oxide layer 2 and the portion of thesilicon oxide layer 52 exposed via the through-hole 511 are removed byperforming a process, similar to that employed in the third embodiment,on the SOI substrate 5. FIG. 5(e) shows the structure obtained at thisstage of the process.

[0104] A silicon oxide layer 3 with a uniform thickness is then formedin a similar manner to the third embodiment such that the entire surfaceof the SOI substrate 5, including the walls 511 a of the through-hole511 and the walls of the through-holes 532, is covered with the siliconoxide layer 3. FIG. 5(e) shows the structure obtained at this stage ofthe process.

[0105] Thus, a mask is obtained which is formed of single crystalsilicon so as to have apertures formed by through-holes 532 whose sizeis content along the whole thickness and have the raised portion 512 inthe peripheral area.

[0106] Because this mask is made of single crystal silicon, even whenthe mask thickness and the opening-to-opening distance are small, themask can be handled without causing bending or deformation. Bending doesnot occur even if no tensile force is applied during the layer formationprocess. The openings can be formed with high enough precision to formhigh-precision pixels.

[0107] In the mask manufactured according to the present embodiment, theapertures corresponding to the thin-layer pattern to be formed areformed by the through-holes 531 formed in the single crystal siliconlayer 53 of the SOI substrate 5, and thus, if the single crystal siliconlayer 53 of the SOI substrate 5 is selected to be thin enough, it ispossible to easily obtain apertures that precisely correspond to thethin-layer pattern to be formed even when the thin-layer pattern has avery small size. Furthermore, as in the third embodiment, the raisedportion 512 may be used in a practically-effective fashion.

[0108] In the technique according to the present embodiment, because thethrough-holes 532 for forming the apertures are manufactured by means ofdry etching, the technique may also be employed when the thin-layerpattern to be formed has a shape other than a square or a rectangle.

[0109] The mask according to the present embodiment does not necessarilyneed to have the silicon oxide layer 3. That is, the final structure ofthe mask may be similar to that shown in FIG. 5(e). Also in this case,by forming the openings 21 in the silicon oxide layer 2 such that theopenings 21 become the same in shape and size as the thin-layer patternto be formed, the through-holes 532 serving as apertures can be easilyobtained which are the same in shape and size as the thin-layer patternto be formed.

[0110] [Method of Manufacturing a Mask According to a Fifth Embodiment]

[0111] A mask and a method of manufacturing it according to a fifthembodiment of the present invention are described below with referenceto FIG. 6.

[0112] In this embodiment, as in the second embodiment, a structure suchas that shown in FIG. 6(a) is formed via process steps shown in FIGS.2(a) to 2(d). Thereafter, square-shaped openings 21 corresponding toapertures to be formed are formed in the silicon oxide layer 2 on thesame side of the thin portion 13 as the raised portion 12. FIG. 6(b)shows the structure obtained at this stage of the process.

[0113] The wafer 1 is then soaked in an aqueous solution of potassiumhydroxide for a predetermined time so that the silicon surface exposedvia the openings 21 is anisotropically wet-etched using etching propertydependence on the crystal orientation. As a result, through-holes 11each having (111)-oriented walls 11 a are formed in the wafer 1, atlocations corresponding to the openings 21. FIG. 6(c) shows thestructure obtained at this stage of the process.

[0114] The silicon oxide layer 2 is then removed by performing aprocess, similar to that employed in the second embodiment, on the wafer1. FIG. 6(d) shows the structure obtained at this stage of the process.A silicon oxide layer 3 with a uniform thickness is then formed in asimilar manner to the second embodiment such that the entire surface ofthe wafer 1, including the walls 11 a of the respective through-holes 11and the bottom of the recessed portion 12, is covered with the siliconoxide layer 3. FIG. 6(e) shows the structure obtained at this stage ofthe process.

[0115] Thus a mask is obtained which is similar in structure to the maskaccording to the second embodiment described above except that theraised portion 14 is located on the same side as that where thethrough-holes 11 have greater aperture sizes than on the opposite side.

[0116] A mask having a structure similar to that obtained in thisembodiment can also be manufactured using an SOI substrate. In thiscase, an SOI substrate 5 similar to that used in the third embodimentmay be employed. After anisotropically wet-etching the single crystalsilicon substrate 51 such that a peripheral portion 512 remains,openings 21 are formed in the silicon oxide layer 52, and through-holes531 are formed in the single crystal silicon layer 53, at locationscorresponding to the openings 21, by means of anisotropic wet etching.

[0117] [Method of Manufacturing a Mask According to a Sixth Embodiment]

[0118] A mask and a method of manufacturing it according to a sixthembodiment of the present invention are described below with referenceto FIG. 7

[0119] In this embodiment, as in the first embodiment described above, asilicon oxide layer 2 is first formed over the entire surface of a wafer1, and then square-shaped openings 21 corresponding to mask apertures tobe formed are formed in the silicon oxide layer 2 on the upper side.FIG. 7(a) shows the structure obtained at this stage of the process.

[0120] The wafer 1 is then soaked in an aqueous solution of potassiumhydroxide for a predetermined time so that the silicon surface exposedvia the openings 21 is wet-etched in a crystal orientation-dependentanisotropic fashion. Herein, the time during which the wafer 1 is soakedin the aqueous solution of potassium hydroxide is selected such that thewafer 1 is etched by a predetermined amount in the thickness direction(so that the portion remaining at the bottom of the recess formed byetching has a predetermined thickness equal to, for example, {fraction(1/20)} times the original thickness). In this embodiment, unlike thefirst embodiment in which through-holes 11 are formed, recessed portions16 having a tapered structure with (111)-oriented walls 16 a are formedin the wafer 1, at locations corresponding to the openings 21, andsilicon 10 remains below each recessed portion 16. FIG. 7(b) shows thestructure obtained at this stage of the process.

[0121] Thereafter, a silicon oxide layer 2 b is formed such that thewalls and the bottom of each recessed portion 16 are covered with thesilicon oxide layer 2 b, and openings 23 are formed in the silicon oxidelayer 2 on the lower side (opposite to the side where the openings 21are formed) such that the opening 23 has a square shape smaller in sizethan the corresponding openings 21 and such that the center of eachopening 23 becomes coincident with the center of the correspondingopening 21. FIG. 7(c) shows the structure obtained at this stage of theprocess.

[0122] The wafer 1 is then soaked in an aqueous solution of potassiumhydroxide for a predetermined time so that the silicon 10 exposed viathe openings 23 is anisotropically wet-etched in (111)-directions untilthe silicon oxide layer 2 b is exposed. As a result, tapered holes 17with (111)-oriented walls 17 a are formed in the wafer 1, at locationscorresponding to the openings 23. The walls of each hole 17 are taperedin opposite directions to directions in which the walls of thecorresponding recessed portion 16 are tapered. FIG. 7(d) shows thestructure obtained at this stage of the process.

[0123] Thereafter, the silicon oxide layers 2 and 2 b are removed by aprocess similar to that employed in the first embodiment so that eachhole 17 communicate with the corresponding recessed portion 16 therebyforming through-holes 18 serving as apertures. FIG. 7(e) shows thestructure obtained at this stage of the process.

[0124] In order to use the resultant structure as a mask in such amanner that the mask is placed such that the lower side (where the holes17 of the through-holes 18 are located) of the wafer is brought intoproximity to a substrate surface on which a thin-layer pattern is to beformed, it is required that the size of each opening 23 that determinesthe size of the corresponding hole 17 should correspond to thethin-layer pattern to be formed. Preferably, the size of each opening 23is determined so that the hole 17 and the corresponding recessed portion16 become equal in size at the boundary between the hole 17 and thecorresponding recessed portion 16.

[0125] A silicon oxide layer 3 with a uniform thickness is then formedin a similar manner to the first embodiment such that the entire surfaceof the silicon wafer 1, including the walls of the respectivethrough-holes 18, is covered with the silicon oxide layer 3. FIG. 7(f)shows the structure obtained at this stage of the process.

[0126] Thus, a mask is obtained which is made of single crystal siliconso as to have a mask surface formed by a (100)-surface of the singlecrystal silicon and have apertures with walls oriented in(111)-directions formed by through-holes 18. In this mask, an open endportion, to be located in proximity to the substrate on which thethin-layer pattern is to be formed, of each through-hole 18 is taperedat an obtuse angle α.

[0127] Therefore, the mask manufactured according to the presentembodiment has, in addition to the advantages similar to those of themask according to the first embodiment, an advantage that an edgeportion of each through-hole 18 on the side to be brought in proximityto the substrate on which the thin-layer pattern is to be formed isprevented from being easily broken.

[0128] The mask according to the present embodiment does not necessarilyneed to have the silicon oxide layer 3. That is, the final structure ofthe mask may be similar to that shown in FIG. 7(e).

[0129] [Embodiment of a Method of Manufacturing an Organic EL Device]

[0130] A first embodiment of a method of manufacturing an organic ELdevice according to the present invention is described below withreference to FIG. 8.

[0131] In this embodiment, by way of example, a process step of formingR (red), G (green), and B (blue) luminescent layers in pixels by meansof vacuum evaporation, included in a process of manufacturing afull-color active matrix organic EL display device, is described.Herein, it is assumed that, before this step, the steps of formingtransistors and capacitors of respective pixels, interconnections amongthem, a driving circuit, and other necessary elements on a glasssubstrate, forming a transparent electrode on each pixel, and, ifnecessary, forming a hole transportation/injection layer on eachtransparent electrode have been performed.

[0132] After performing the above-described steps in a known manner, theglass substrate 6 is placed on a substrate holder 7 in a vacuumevaporator, and a mask 9 is placed thereon via a mask holder 8.

[0133] In this display device to be manufactured, pixels are arranged atregular intervals in the order of R, G, B, R, G, B, and so on in adirection parallel with a side of the glass substrate. The mask 9 has asmany apertures 91 as there are sets of R, G, and B pixels, wherein theapertures 91 are formed at locations corresponding to the respectivesets of R, G, and B pixels.

[0134] The mask 9 may be formed of single crystal silicon so as to havea mask surface formed by a (100)-surface of the single crystal siliconand have apertures 91 formed by tapered through-holes with(111)-oriented walls. Such a mask may be manufactured in accordance withone of the embodiments described above (other than the fourthembodiment). However, in the present embodiment, the raised portion inthe peripheral area of the mask is removed.

[0135] The mask holder 8 has the form of a frame. A peripheral area witha predetermined width on the glass substrate, outside an area in which athin layer is to be formed, is covered by the frame-shaped mask holder8. The thickness of the mask holder 8 is selected to be equal to the sumof the thickness of the thin layer to be formed and the gap between themask and the thin layer (for example, the thickness of the mask holder 8is selected to be 2 μm). The mask 9 is placed on the mask holder 8 suchthat a mask surface at which the apertures 91 are smaller than at theopposite surface is brought into proximity to the glass substrate (onwhich the thin layer is to be formed).

[0136] Thereafter, the mask position is adjusted so that the maskapertures 91 come to locations where R pixels are to be formed, and atarget material for forming an R (red) luminescent layer is evaporated.As a result, a red luminescent layer 61 is formed on the glass substrate6, at locations of R pixels. FIG. 8(a) shows the structure obtained atthis stage of the process.

[0137] Thereafter, the mask 9 is displaced in a horizontal direction bya distance corresponding to one pixel so that the apertures 91 come tolocations of G pixels adjacent to the R pixels, and a target materialfor forming a G (green) luminescent layer is evaporated. As a result, agreen luminescent layer 62 is formed on the glass substrate 6, atlocations of G pixels. FIG. 8(b) shows the structure obtained at thisstage of the process.

[0138] Thereafter, the mask 9 is further displaced in the horizontaldirection by a distance corresponding to one pixel so that the apertures91 come to locations of B pixels adjacent to the G pixels and a targetmaterial for forming a B (blue) luminescent layer is evaporated. As aresult, a blue luminescent layer 63 is formed on the glass substrate 6,at locations of B pixels. FIG. 8(c) shows the structure obtained at thisstage of the process.

[0139] After forming the luminescent layers, the following steps offorming a cathode layer and other necessary elements are performedaccording to a known method so as to obtain a full-color active matrixorganic EL display device.

[0140] In the present embodiment, because the mask 9 can be formed ofsingle crystal silicon so that the apertures 91 precisely correspond topixels with a very small size, the resultant full-color active matrixorganic EL display device has high-precision pixels.

[0141] Furthermore, because the mask 9 having apertures 91 formed by thetapered through-holes is placed in the above-described manner, eachluminescent layer is prevented from becoming thin at pattern edges.Thus, good uniformity of the luminescent intensity of the pixels isobtained over the entire surface of the glass substrate 6.

[0142] A second embodiment of a method of manufacturing an organic ELdevice according to the present invention is described below withreference to FIG. 9.

[0143] In this embodiment, different masks 9A, 9B, and 9C are used toform R, G, and B pixels. The mask 9A for forming R pixels has apertures91A formed at locations corresponding to the locations of R pixels, themask 9B for forming G pixels has apertures 91B formed at locationscorresponding to the locations of G pixels, and the mask 9C for formingB pixels has apertures 91C formed at locations corresponding to thelocations of B pixels. These masks 9A, 9B, and 9C are basically similarthe mask 9 shown in FIG. 8 except that the apertures 91A to 91C areformed at different locations.

[0144] In the present embodiment, a glass substrate 6 is placed in abox-shaped substrate holder 71 having an inner depth greater than thethickness of the glass substrate 6 and a step serving as a masksupporting plane 72 is formed on the top surface of box wall. The masksupporting plane 72 is formed such that when the mask is placed thereon,a gap equal to the sum of the thickness of a thin layer to be formed anda gap between the surface of the thin layer and the mask surface isformed between the upper surface of the glass substrate 6 and the lowersurface of the mask (for example, the gap is selected to be 18 μm).

[0145] First, the glass substrate 6 is placed in the substrate holder71, and then the mask 9A for forming R pixels is placed on the maskholding plane 72. Thereafter, a target material for forming an R (red)luminescent layer is evaporated. As a result, a red luminescent layer 61is formed on the glass substrate 6, at locations of R pixels. FIG. 9(a)shows the structure obtained at this stage of the process.

[0146] The mask 9A is removed, and the mask 9B is placed on the masksupporting plane 72. Thereafter, a target material for forming a G(green) luminescent layer is evaporated. As a result, a greenluminescent layer 62 is formed on the glass substrate 6, at locations ofG pixels. FIG. 9(b) shows the structure obtained at this stage of theprocess.

[0147] The mask 9B is removed, and the mask 9C is placed on the masksupporting plane 72. Thereafter; a target material for forming a B(blue) luminescent layer is evaporated. As a result, a blue luminescentlayer 63 is formed on the glass substrate 6, at locations of B pixels.FIG. 9(c) shows the structure obtained at this stage of the process.

[0148] In addition to the advantages obtained when the mask 9 shown inFIG. 8 is used, the method according to the present embodiment has afurther advantage that R, G, and B pixels can be manufactured using thedifferent masks 9A to 9C instead of moving the single mask, and thus theproduction process becomes simple compared with the process using onlythe mask 9 shown in FIG. 8.

[0149] Apertures formed by anisotropically etching a single crystalsilicon substrate or a single crystal silicon layer on an SOI substrateare so precise in size that size differences in apertures from mask tomask can be neglected. This means that a thin-layer pattern can bemanufactured using different masks for different color pixels withoutcausing a significant size difference among different color pixels.

[0150] In the embodiments shown in FIGS. 8 and 9, the raised portion 14or 512 formed on the mask manufactured according to the second, third,or fifth embodiment is removed. However, in the case where the raisedportion 14 or 512 is formed on the same side as the side where thethrough-holes 11 or 531 have smaller aperture sizes than on the oppositeside as is in the mask according to the second or third embodiment, theraised portion 14 or 512 is located on the same side (back side of themask) as that brought into proximity to a substrate surface on which athin-layer pattern is to be formed, and the raised portion 14 or 512 maybe used in an effective manner as described below with reference toFIGS. 10 and 11.

[0151] In the example shown in FIG. 10, the raised portion formed in theperipheral area on the back side of the mask 9 is etched so as to have ashape similar to the mask holder 8 shown in FIG. 8 thereby allowing theraised portion to serve as the mask holder 92. That is, in this case,the mask holder 92 is formed in an integral fashion with the mask 9.

[0152] In the example shown in FIG. 11, a stepped surface (substratesupporting plane) 93 a for supporting the glass substrate 6 is formed onthe raised portion 9 in the peripheral area on the back side of themask. In this example, the glass substrate 6 is placed above the mask 9by positioning the glass substrate 6 on the substrate supporting plane93 a of the mask 9), and a layer is deposited from below through themask 9. In this case, therefore, the mask 9 is needed to be supported bya frame-shaped mask holder 75 such that the lower surface of the mask 9is exposed except for the peripheral portion covered by the frame-shapedmask holder 75.

[0153] [Seventh Embodiment]

[0154] A seventh embodiment of a mask according to the present inventionis described below with reference to FIG. 12.

[0155]FIG. 12(a) is a plan view of the mask according to the seventhembodiment of the present invention, and the FIG. 12(b) is across-sectional view taken along a line B-B of FIG. 12(a).

[0156] This mask has a thin portion 13 formed in the center thereof anda raised portion (thick portion) 14 formed on the edge thereof, whereinapertures 110 are formed in the thin portion 13 while no mask aperturesare formed in the raised portion 14. The apertures 110 are formed in thethin portion 13 by through-holes extending in a direction perpendicularto the mask surface. The size of each through-hole 110 is minimum at apredetermined position (at the boundary) C in the thickness direction ofthe mask and increases toward both mask surfaces. The shape of eachaperture 110, in cross section parallel with the mask surface, is squareover the entire thickness of the mask.

[0157] Each aperture 110 is formed by a first tapered hole 111 on thesame side as the raised portion 14 and a second tapered hole 112 on theopposite side wherein the first and second tapered holes 111 and 112communicate with each other and the first tapered hole 111 and thesecond tapered hole 112 are tapered in opposite directions. The aperturesize W0, at the boundary C, of each aperture 110 is selected to be equalto the size of the thin-layer pattern to be formed, and the size W1 ofthe first tapered hole 111 at the mask surface and the size W2 of thesecond tapered hole 112 at the opposite mask surface are greater thanthe size W0 at the boundary C.

[0158] The first tapered hole 111 is formed by four walls 111 a taperedat an acute angle θ1 (for example 54.74°) to the mask surface. Thesecond tapered hole 112 is formed by four walls 112 a tapered at anacute angle θ2 (for example 70°) to the mask surface. Thus, the anglesof edges 13 a and 13 b of the apertures (that is, angles of the walls111 a and 112 a with respect to the mask surface of the thin portion 13)are obtuse at both mask surfaces (α1>90° and α2>90°) The distance t1from the boundary C to the mask surface on the same side as the raisedportion 14 (that is, the depth of the first tapered hole 111) isdifferent from the distance t2 from the boundary C to the mask surfaceon the side opposite to the raised portion 14 (that is, the depth of thesecond tapered hole 112). That is, because the mask is placed such thatthe mask surface opposite to the raised portion 14 is brought intoproximity to a substrate on which a layer is to be formed, the distancet2 (depth of the second tapered hole 112) is set to be smaller than thedistance t1. The smaller the depth (distance t2) of the tapered hole ofeach aperture on the side in proximity to the substrate on which thelayer is to be formed, the more accurate the pattern size of theresultant thin layer.

[0159] The advantages of the mask according to the seventh embodimentcompared with the mask according to the fifth embodiment shown in FIG.6(d) are discussed below.

[0160] In the case of the mask according to the fifth embodiment, theangle of an edge portion of each aperture (that is, an angle between thewall 11 a and a mask surface of the thin portion 13) is obtuse at thesurface on the side of the recessed portion 12 and acute at the oppositesurface.

[0161] If this mask is placed such that the side where the aperture edgeangles are acute (the side where the apertures have smaller aperturesizes than on the opposite side) is brought into proximity to asubstrate surface on which a thin-layer pattern is to be formed, itbecomes possible to prevent the resultant thin-layer pattern frombecoming thin at its edge, and thus the resultant thin-layer pattern hashigh size accuracy. However, a problem is that an acute edge 13 c ofeach aperture is easily broken during the process. If the mask is placedsuch that the side where obtuse edges are located (where apertures havegreater aperture sizes than on the opposite side) is brought intoproximity to a substrate surface on which a thin-layer is to be formed,edges 13 d of apertures not easily broken during the process because theedges 13 d are obtuse. However, the resultant thin-layer pattern doesnot have high size accuracy, unless the thickness of the thin portion 13is reduced to an extremely small level. The reduction in the thicknessof the thin portion 13 to an extremely small level results in areduction in the mechanical strength and thus can cause the apertures 11to be deformed.

[0162] In contrast, in the mask according to the seventh embodiment, theedges 13 a and 13 b of the apertures are obtuse at both mask surfaces,and thus the mask edges 13 b are not easily broken even if the sidewhere the second tapered holes 112 are located (the side where thedistance to the boundary position C is smaller than the opposite side)is brought into proximity to a substrate surface on which a thin-layerpattern is to be formed. Furthermore, because each aperture 110 isformed of a first tapered hole 111 and a second tapered hole 112, thedepth t2 of the second tapered hole 112 can be reduced to an extremelysmall level without having to reduce the thickness of the thin portion13. This makes it possible to manufacture a thin-layer pattern havinghigh size accuracy without causing a reduction in the mechanicalstrength of the thin portion 13 and thus it becomes possible to preventedges of apertures from being broken during use.

[0163] Examples of methods of manufacturing such a mask are describedbelow. A first method is described first with reference to FIG. 13.

[0164] First, a structure similar to that shown in FIG. 13(a) ismanufactured by performing steps similar to those shown in FIGS. 2(a) to2(d) according to the second embodiment.

[0165] Thereafter, square-shaped openings 211 in the form ofthrough-holes are manufactured in the silicon oxide layer 2 on the firstsurface (on the same side as that where the recessed portion 12 isformed) of the thin portion 13, at locations corresponding to thelocations of apertures 110 such that the aperture size of each opening211 will become equal to the size W1 of the corresponding first taperedhole 111 at the mask surface. FIG. 13(b) shows the structure obtained atthis stage of the process.

[0166] The wafer 1 is then soaked in an aqueous solution of potassiumhydroxide for a predetermined time so that the silicon surface exposedvia the openings 211 is wet-etched in a crystal orientation-dependentanisotropic fashion. As a result, tapered through-holes (first taperedholes) 111 having (111)-oriented walls 111 a are formed at locationscorresponding to the openings 211. FIG. 13(c) shows the structureobtained at this stage of the process.

[0167] Thereafter, square-shaped openings 212 in the form ofthrough-holes are manufactured in the silicon oxide layer 2 on thesecond surface (opposite to the first surface) of the thin portion 13,at locations corresponding to the locations of apertures 110 such thatthe aperture size of each opening 212 will become equal to the size W2(>W0) of the corresponding second tapered hole 112 at the mask surface.FIG. 13(d) shows the structure obtained at this stage of the process.

[0168] The size W1 of the first tapered hole 111 at the first surface isdetermined taking into account the thickness of the thin portion 13 suchthat the size W0 of the aperture 110 at the boundary position C willbecome equal to the size of the thin-layer pattern to be formed. Thismeans that, at the stage shown in FIG. 13(c), the size W3 of the firsttapered hole 111 at the second surface is smaller than the size W0 atthe boundary position C. That is, at the stage of the process shown inFIG. 13(d), the edges 13 e of the thin portion 13 are exposed via theopenings 212 formed in the silicon oxide layer 2 formed on the secondsurface.

[0169] Thereafter, the wafer 1 is soaked in an aqueous solution ofpotassium hydroxide for a predetermined time so that the edges 13 e ofthe thin portion 13 exposed via the openings 212 are wet-etched in acrystal orientation-dependent anisotropic fashion. As a result, secondtapered holes 112 having walls 112 a oriented in particular crystalorientation of the single crystal silicon are formed such that eachsecond tapered holes 112 communicate with a corresponding first taperedhole 111. FIG. 13(e) shows the structure obtained at this stage of theprocess.

[0170] Note that, in this method, it is required that the soaking timeshould be precisely controlled such that the etching is ended at theboundary position C. Also note that the walls 112 a formed by thepresent method are not necessarily oriented in (111) directions.

[0171] The silicon oxide layer 2 is then removed by performing aprocess, similar to that employed in the second embodiment, on the wafer1. FIG. 13(f) shows the structure obtained at this stage of the process.

[0172] The resultant mask obtained by the present method has a structuresuch as that shown in FIG. 12, formed of single crystal silicon suchthat the mask surface is formed by a (100) surface of the single crystalsilicon, each aperture 110 has two wall portions 111 a and 112 a thattapered in opposite directions and that expand toward respective masksurfaces opposite to each other, and at least the wall portion 111 a ofthe first tapered hole 111 is oriented in a (111) direction.

[0173] Now, a second method of manufacturing a mask according to theseventh embodiment is described below with reference to FIG. 14.

[0174] First, a structure similar shown in FIG. 14(a) is manufactured byperforming steps similar to those shown in FIGS. 2(a) to 2(d) accordingto the second embodiment.

[0175] Thereafter, square-shaped openings 211 in the form ofthrough-holes are manufactured in the silicon oxide layer 2 on the firstsurface (on the same side as that where the recessed portion 12 isformed) of the thin portion 13, at locations corresponding to thelocations of apertures 110 such that the aperture size of each opening211 will become equal to the size W1 of the corresponding first taperedhole 111 at the mask surface. Thereafter, square-shaped recessedportions 221 are formed in the silicon oxide layer 2 on the secondsurface (opposite to the first surface) of the thin portion 13, atlocations corresponding to the locations of apertures 110 such that thesize of each recessed portion 221 will become equal to the size W2 (>W0)of the corresponding second tapered hole 112 at the mask surface.

[0176] Thus, a first protective layer pattern 210 having through-holes211 corresponding to the apertures 110 is formed on the first surface ofthe thin portion 13, and a second protective layer pattern 220 havingrecessed portions 221 corresponding to the apertures 110 is formed onthe second surface of the thin portion 13. FIG. 14(b) shows thestructure obtained at this stage of the process.

[0177] The wafer 1 is then soaked in an aqueous solution of potassiumhydroxide for a predetermined time so that the silicon surface exposedvia the openings 211 is wet-etched in a crystal orientation-dependentanisotropic fashion. As a result, tapered through-holes (first taperedholes) 111 with walls 111 a oriented in (111)-directions are formed inthe wafer 1, at locations corresponding to the openings 211. FIG. 14(c)shows the structure obtained at this stage of the process.

[0178] The wafer 1 is then soaked in an aqueous solution of potassiumhydroxide for a predetermined time so that the silicon oxide layer 2 isremoved by an amount corresponding to the thickness of the bottomportion 221 a of the recesses 221. As a result, the recesses 221 becomethrough-holes 222 and thus the second protective layer pattern 220becomes a third protective layer pattern 230, as shown in FIG. 14(d).The first protective layer pattern 210 remains in a state in which thethickness is uniformly decreased by an amount corresponding to thethickness of the bottom portion 221 a. That is, the original thicknessof the silicon oxide layer 2 is selected such that the silicon oxidelayer 2 remains on the first surface at this stage of the process.

[0179] The size W1 of the first tapered hole 111 at the first surface isdetermined taking into account the thickness of the thin portion 13 suchthat the size W0 of the aperture 110 at the boundary position C willbecome equal to the size of the thin-layer pattern to be formed. Thismeans that, at the stage shown in FIG. 14(c), the size W3 of the firsttapered hole 111 at the second surface is smaller than the size W0 atthe boundary position C. That is, at the stage of the process shown inFIG. 14(d), the edges 13 e of the thin portion 13 are exposed via thethrough-holes (openings formed in the silicon oxide layer 2 on thesecond surface) of the third protective layer pattern 230.

[0180] Thereafter, the wafer 1 is soaked in an aqueous solution ofpotassium hydroxide for a predetermined time so that the edges 13 e ofthe thin portion 13 exposed via the openings 222 are wet-etched in acrystal orientation-dependent anisotropic fashion. As a result, secondtapered holes 112 having walls 112 a oriented in particular crystalorientation of the single crystal silicon are formed such that eachsecond tapered holes 112 communicate with a corresponding first taperedhole 111. FIG. 14(e) shows the structure obtained at this stage of theprocess.

[0181] Note that, in this method, it is required that the soaking timeshould be precisely controlled such that the etching is ended at theboundary position C. Also note that the walls 112 a formed by thepresent method are not necessarily oriented in (111) directions.

[0182] The silicon oxide layer 2 is then removed by performing aprocess, similar to that employed in the second embodiment, on the wafer1. FIG. 14(f) shows the structure obtained at this stage of the process.

[0183] As with the mask manufactured according to the first methoddescribed above, the resultant mask obtained by the present method has astructure such as that shown in FIG. 12, formed of single crystalsilicon such that the mask surface is formed by a (100) surface of thesingle crystal silicon, each aperture 110 has two wall portions 111 aand 112 a that tapered in opposite directions and that expand towardrespective mask surfaces opposite to each other, and at least the wallportion 111 a of the first tapered hole 111 is oriented in a (111)direction.

[0184] In the second method, in contrast to the first method in whichthe patterning of the silicon oxide layer 2 on the second surface isperformed after forming the through-holes 111 in the thin portion 13,the patterning is performed before forming the through-holes 111 in thethin portion 13. If the patterning of the silicon oxide layer 2 isperformed after forming the through-holes 111, breakage often occursduring a photolithographic process. Thus, the second method has higherproductivity than the first method.

[0185] In the first and second methods described above, the patterningof the silicon oxide layer 2 may be performed by a conjunction of aphotolithography process using a positive resist and a wet etchingprocess using a buffer solution of hydrofluoric acid (BHF, such as amixture of a 50 wt % HF aqueous solution and a 45 wt % NH₄F of a volumeratio of 1:6).

[0186] [Third Embodiment of a Method of Manufacturing an Organic ELDevice]

[0187] A third embodiment of a method of manufacturing an organic ELdevice according to the present invention is described below withreference to FIGS. 15 to 17.

[0188] In this embodiment, by way of example, a process step of formingR (red), G (green), and B (blue) luminescent layers in pixels by meansof vacuum evaporation, included in a process of manufacturing afull-color active matrix organic EL display device, is described.

[0189] First, after forming transistors 302 and capacitors of respectivepixels, interconnections among them, a driving circuit, and othernecessary elements on a glass substrate 301, a first electrode 303 foreach pixel is formed, and a first insulating layer 304 is formed inareas other than the first electrode 303. Thereafter, a mask 90 isplaced on the glass substrate 301 via a mask holder 8.

[0190] In this display device to be manufactured, pixels are arranged atregular intervals in the order of R, G, B, R, G, B, and so on in adirection parallel with a side of the glass substrate. The mask 90 hasas many apertures 110 as there are sets of R, G, and B pixels, whereinthe apertures 110 are formed at locations corresponding to therespective sets of R, G, and B pixels. The mask 90 may be a mask that ismanufactured according to the seventh embodiment described above (usingsingle crystal silicon so as to have apertures 110 each composed of afirst tapered hole 111 and a second tapered hole 112). In this case, themask 90 is placed such that the size where the second tapered holes 112are located is brought into proximity to the glass substrate 301.

[0191] After positioning the mask 90 such that the apertures 110 come tolocations where R pixels should be formed, a target material for formingan R (red) luminescent layer is evaporated. As a result, a redluminescent layer 61 is formed on the first electrode 303 on the glasssubstrate 301, at locations of R pixels. FIG. 15 shows the structureobtained at this stage of the process. The above process ofmanufacturing the red luminescent layer 61 may be performed, forexample, by first forming m-MTDATA serving as a hole injection layer,then forming α-NPD serving as a hole transportation layer, furtherforming BSB—BCN serving as a luminescent layer, and finally forming Alq3serving as an electron transportation layer.

[0192] The mask 90 is then displaced in a horizontal direction by adistance corresponding to one pixel such that the apertures 110 come tolocations of G pixels adjacent to the R pixels, and a target materialfor forming a G (green) luminescent layer is evaporated. As a result, agreen luminescent layer 62 is formed on each first electrode 303 on theglass substrate 301, at locations of G pixels. The above process ofmanufacturing the green luminescent layer 62 may be performed, forexample, by first forming m-MTDATA serving as a hole injection layer,then forming α-NPD serving as a hole transportation layer, and finallyforming Alq3 serving as a luminescent layer and also as an electrontransportation layer.

[0193] The mask 90 is then further displaced in the horizontal directionby a distance corresponding to one pixel such that the apertures 110come to locations of G pixels adjacent to the R pixels, and a targetmaterial for forming a B (blue) luminescent layer is evaporated. As aresult, a blue luminescent layer 63 is formed on each first electrode303 on the glass substrate 301, at locations of B pixels. FIG. 16 showsthe structure obtained at this stage of the process. The above processof manufacturing the blue luminescent layer 63 may be performed, forexample, by first forming m-MTDATA serving as a hole injection layer,then forming α-NPD serving as a hole transportation layer, furtherforming bathocuproine (2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline)serving as a luminescent layer and also as a hole block layer, andfinally forming Alq3 serving as a luminescent layer.

[0194] Thereafter, second electrode layer 305 is formed on the glasssubstrate 301 by means of vacuum evaporation. FIG. 17 shows thestructure obtained at this stage of the process. If necessary, the upperside of the second electrode layer 305 is sealed.

[0195] In the present embodiment, because the mask 90 can be formed ofsingle crystal silicon so that the apertures 110 precisely correspond topixels with a very small size, the resultant full-color active matrixorganic EL display device has high-precision pixels.

[0196] Furthermore, because the mask 90 having apertures 110 eachcomposed of the first tapered hole 111 and the second tapered hole 112is placed in the above-described manner, each luminescent layer isprevented from becoming thin at pattern edges. Thus, good uniformity ofthe luminescent intensity of the pixels is obtained over the entiresurface of the glass substrate 6. Furthermore, the mask has a highmechanical strength, and thus it is possible to prevent edges ofapertures from being broken during use.

[0197] [Fourth Embodiment of a Method of Manufacturing an Organic ELDevice]

[0198] A fourth embodiment of a method of manufacturing an organic ELdevice according to the present invention is described below withreference to FIGS. 18 to 22.

[0199] In this embodiment, first, transistors 302 and capacitors ofrespective pixels, interconnections among them, a driving circuit, andother necessary elements are first formed on a glass substrate 301, andthen a first electrode 303 for each pixel is formed. Thereafter, a firstinsulating layer 304 is formed on the first electrodes 303. The firstinsulating layer 304 is patterned so that pixel openings 304 a areformed at locations corresponding to the respective first electrodes303. FIG. 18 shows the structure obtained at this stage of the process.

[0200] Thereafter, a second insulating layer 306 having openings 306 a,formed at locations corresponding to the locations of the firstelectrodes 303 so as to have a greater size than the pixel openings 304a, is formed on the first insulating layer 304 such that the secondinsulting layer 306 has a thickness greater enough than the thickness ofany luminescent layer. FIG. 19 shows the structure obtained at thisstage of the process. A mask 900 is then placed on the glass substratesuch that the mask 900 is brought into contact with the secondinsulating layer 306.

[0201] In this display device to be manufactured, pixels are arranged atregular intervals in the order of R, G, B, R, G, B, and so on in adirection parallel with a side of the glass substrate. The mask 900 hasas many apertures 901 as there are sets of R, G, and B pixels, whereinthe apertures 901 are formed at locations corresponding to therespective sets of R, G, and B pixels.

[0202] The mask 900 may be formed of single crystal silicon so as tohave a mask surface formed by a (100)-surface of the single crystalsilicon and have apertures 901 formed by tapered through-holes with(111)-oriented walls. Such a mask may be manufactured in accordance withone of the embodiments described above (other than the fourthembodiment). However, in the present embodiment, the raised portion inthe peripheral area of the mask is removed. The mask 900 is placed suchthat the mask surface at which the apertures 901 have greater aperturesizes than at the opposite mask surface is brought into proximity to theglass substrate.

[0203] After positioning the mask 900 such that the apertures 901 cometo locations where R pixels should be formed, a target material forforming an R (red) luminescent layer is evaporated. As a result, a redluminescent layer 61 is formed on the first electrode 303 on the glasssubstrate 301, at locations of R pixels. Thereafter, the mask 900 isdisplaced in the horizontal direction by a distance corresponding to onepixel, and a target material for forming a G (green) luminescent layeris evaporated thereby forming a green luminescent layer 62. A blueluminescent layer 63 is then formed in a similar manner. The luminescentlayers 61 to 63 are formed on the respective electrodes 303 so as to bethicker than the first insulating layer 304. FIG. 21 shows the structureobtained at this stage of the process.

[0204] Thereafter, a second electrode layer 305 is formed on the glasssubstrate 301 by means of vacuum evaporation. FIG. 22 shows thestructure obtained at this stage of the process. If necessary, the upperside of the second electrode layer 305 is sealed.

[0205] In this method, the accuracy of the size of each pixel isdetermined by the accuracy of the size of the corresponding pixelopening 304 a. Therefore, the placing the mask 900 such that the masksurface at which the openings 901 have an obtuse angle (greater aperturesize) is brought into proximity to the glass substrate does not cause areduction in the accuracy of the size of the pixels. If the mask 900 isplaced in such a manner, it is possible to prevent edges of the openingsfrom being broken.

[0206] Although in the embodiments described above, the anisotropic wetetching of single crystal silicon is performed using an aqueous solutionof potassium hydroxide, another alkali solution such as an aqueoussolution of tetramethylammoniumhydroxide or an aqueous solution ofethylenediaminepyrocatechol may also be employed. In the case where anaqueous solution of potassium hydroxide is employed, the concentrationis preferably selected within the range from 2 to 40 wt % and morepreferably from 10 to 30 wt %.

[0207] In particular, when the mask is used to manufacture an activematrix organic EL device, it is desirable to use an aqueous solution oftetramethylammoniumhydroxide or (with a concentration of 20 to 30 wt %at a temperature higher than 80°) to avoid contamination with alkalimetal.

[0208] In the embodiments described above, the mask according to thepresent invention is used as a vacuum evaporation mask. The maskaccording to the present invention may also be used to directly form athin-layer pattern using a method (such as sputtering, ion plating,etc.) other than vacuum evaporation.

[0209] Organic EL devices can be used in a wide variety of electronicdevices such a mobile personal computer, a portable telephone, and adigital still camera.

[0210]FIG. 23 is a perspective view illustrating the structure of amobile personal computer.

[0211] In FIG. 23, the personal computer 100 includes a main part 104having a keyboard 102 and a display unit 106 using an organicelectroluminescence device.

[0212]FIG. 24 is a perspective view of a portable telephone. In FIG. 24,the portable telephone 200 includes a plurality of operation controlbuttons 202, an earpiece 204, a mouthpiece 206, and a display panel 208using an organic electroluminescence device.

[0213] In addition to the personal computer shown in FIG. 23, theportable telephone shown in FIG. 24, and a digital still camera shown,the organic electroluminescence display device according to the presentinvention may also be used in other various electronic devices such as atelevision, a video tape recorder with a viewfinder or a monitor, a carnavigation device, a pager, an electronic notepad, a calculator, a wordprocessor, a workstation, a video telephone, a POS terminal, and adevice including a touch panel.

[0214] In the mask according to the present invention, as describedabove, apertures have high enough accuracy to form high-precision pixelswithout causing the mask to be bent or deformed and without having toapplying a tensile force to the mask during a thin-layer formationprocess. Thus, the mask can be used to manufacture a thin-layer patternof high-precision pixels of an organic EL device.

[0215] The mask production method according to the present inventionmakes it possible to manufacture a having apertures with high enoughaccuracy to form high-precision pixels without causing the mask to bebent or deformed and without having to applying a tensile force to themask during a thin-layer formation process.

[0216] Furthermore, according to the organic EL device production methodof the present invention, a high-precision thin-layer pattern serving asa layer of an organic EL element can be formed by means of vacuumevaporation to manufacture, for example, a high-precision full-coloractive matrix organic EL display device.

[0217] Using an organic EL device according to the present invention, itis possible to manufacture a high-precision full-color active matrixorganic EL display device.

1. A mask for use in manufacturing a thin-layer pattern serving as alayer of an organic electroluminescence element by means of vacuumevaporation, the mask having an aperture corresponding to the thin-layerpattern, the mask being formed of single crystal silicon and having athrough-hole serving as the aperture formed by means of anisotropic wetetching using a crystal orientation dependence.